Joe Lieberman and Ben Nelson cast their last votes in the early morning of New Year’s Day 2013, ending their decades-long careers as centrist Democrats on a bipartisan budget deal.

Both senators had reached the tipping point in their ideological journeys. Lieberman faced a hostile climate among liberals who dominated Democratic politics in Connecticut and Nelson found it virtually impossible to navigate the deeply conservative terrain of Nebraska.

Almost a decade later, the two published books about the rise and fall of centrists, particularly in the Senate, recalling the key roles they played in deals that saved the filibuster, ended a ban on gay people serving in the military and approved the Affordable Care Act.

The negotiations on that latter project, from Thanksgiving to Christmas 2009, serve in some ways as a preview of what’s to come as Senate Democrats attempt in the weeks ahead to reach total unity and pass President Biden’s sweeping social policy agenda worth nearly $2 trillion.

Here’s what you need to know about the procedure’s complicated history meant to delay, delay, delay. (Drea Cornejo/The Washington Post)

Lieberman, now 79 and working at a New York law firm, finds a bit of optimism despite the doom and gloom for centrists. “In some very encouraging ways, the 2020 election can be seen as a centrist uprising against partisan and ideological divisions, harsh personal rhetoric, and the resulting governmental gridlock in Washington,” he writes in “The Centrist Solution.”

Nelson, now 80 and living in Omaha, has a darker view — as his book’s title, “Death of the Senate,” lets on — and worries about whether today’s lawmakers are really willing to put in the hard work to “reach across the aisle” to form a real coalition getting things done.

“It hasn’t happened because it is broken. Not possible. Hopelessly fractured,” Nelson writes.

In separate interviews Thursday and Friday, both men acknowledged that their views will be dismissed by some as impractical and the typical fare of ex-politicians wanting to talk about the good old days.

And today’s Democrats say that it’s next to impossible to work with Republican counterparts who are so loyal to Donald Trump, even after the ex-president’s supporters stormed the Capitol on Jan. 6. Today’s Republicans see their counterparts going with a party-line agenda to transform the social safety net after a 2020 election that left each chamber almost evenly divided.

“These extreme words disallow the opportunity to find exceptions. You just have to work harder. I don’t think that they’re really trying hard enough on either side,” Nelson said in an interview.

Nelson joined Lieberman in the Senate in 2001, when it was also a 50-50 Senate. They often worked across the aisle with GOP partners like the late John McCain (R-Ariz.) and Lindsey Graham (R-S.C.), particularly on a 2005 deal that averted a Republican attempt to blow up the filibuster to quickly confirm George W. Bush’s nominees to the circuit courts.

In his book, Nelson recounts how the group, preserving the filibuster but allowing some Bush nominees quick passage, specifically decided against quick confirmation of Brett M. Kavanaugh to the D.C. Circuit Court of Appeals.

GOP senators in that group felt Kavanaugh lacked the experience for such a prime judicial post, so he waited another year to get confirmed. In the fall of 2018, well into his retirement, Nelson blew up as he watched Graham rally Republicans around Kavanaugh’s elevation to the Supreme Court despite assault allegations as a teenager and a second hearing that degenerated into a display of insults to senators.

“The Lindsay Graham I see on TV today is not the Lindsey Graham I remember,” Nelson writes, suggesting that McCain’s death in 2018 left him without a “moral anchor” and that his drift into Fox News regular and Trump supporter illustrates the end of centrism. “The once-serious workhorses have given in to a culture of grandstanding.”

Lieberman saw up close the early stages of hyper-partisanship, first in his 2006 reelection campaign. He lost the Democratic primary to a previously unheard of challenger, Ned Lamont, who ran hard against Lieberman’s support for the Iraq War. Lieberman won the general election as an independent.

That experience drew him even closer to McCain, who used his support for the war to rally his 2008 presidential chances and win the GOP nomination. After Lieberman’s endorsement, McCain asked him to consider becoming his vice-presidential nominee.

Eventually, McCain’s advisers warned him off Lieberman because conservatives would revolt against a supporter of abortion rights and same-sex marriage on the Republican ticket.

“I came face to face with the partisanship in both major American political parties,” Lieberman writes.

Immediately after Barack Obama’s victory over McCain, then-Senate Majority Leader Harry M. Reid (D-Nev.) told Lieberman that some Democrats wanted to punish him and take away his committee chairmanship.

Lieberman refused and Reid — an intuitively savvy vote-counter — knew he’d rather keep him in his caucus for votes that mattered than let him cross the aisle to join ranks with Senate Minority Leader Mitch McConnell (R-Ky.).

Within weeks Lieberman, Nelson and others hammered out the final details of a roughly $800 billion economic stimulus plan that many Democrats thought was too small but the centrists argued was just right.

When it came to the health law negotiations, those two served to a degree as the Sens. Joe Manchin III (D-W.Va.) and Kyrsten Sinema (D-Ariz.) of this era: the public faces of the crucial votes.

With the House trying to pass Biden’s domestic agenda later this month, Senate Majority Leader Charles E. Schumer (D-N.Y.) will then have to wrangle the last votes out of those current centrist Democrats to get 50 out of 50 in his caucus to win passage.

But Reid had to go 60 for 60 back in 2009 with a group that included at least 10 centrist Democrats. Just as Manchin has voiced opposition to some liberal proposals for months, Lieberman and Nelson did the same — with similar results, as many people refused to listen.

Finally, in mid-December 2009 sitting next to Nelson on CBS’s “Face the Nation,” Lieberman said he would absolutely oppose the ACA if it included a government-run health option to compete against private insurers.

Years later, many liberal activists wrongly still believe Lieberman alone killed this public option, but he was speaking on behalf of at least five Democrats who opposed the plan and made that clear. “It wasn’t even on life support at that time,” Nelson recalled in the interview.

Reid summoned Lieberman to his office for a meeting with White House Chief of Staff Rahm Emanuel, who demanded to know if Lieberman would support the health law otherwise. “Yes, I will enthusiastically support the rest of the bill,” Lieberman said.

“Okay,” Emanuel responded, “the public option is out of the bill.”

Nelson then had to negotiate the final details of the legislation around Medicaid expansion, which led to accusations that he got favorable treatment for his state, and on abortion language. The final language left each state in the similar position, but the phrase “Cornhusker Kickback” became burned into Nelson’s profiles.

Both Lieberman and Nelson remain dismayed that social media today thinks of them as obstacles to Obama’s greatest achievement in domestic policy. “The Affordable Care Act — for which I was the necessary 60th vote — was real and historic health-care reform,” Lieberman writes.

Their experience serves as a warning for how Biden and Schumer might want to handle Manchin, with extreme care. Nelson credits Biden, a 36-year veteran of the Senate, for his somewhat passive role in allowing negotiations to play out as president.

“I think he’s handled Congress as well as anyone could have, given the divisions,” he said.

But Lieberman laments that the president has not been more forceful in pushing for unity. “Not as much as he’s capable of doing,” he said.

A few centrist deals have emerged the past year, including a $900 billion pandemic relief bill and the more than $1 trillion infrastructure Biden will sign into law Monday.

It gives them hope, but the ideological trend lines keep getting further apart since 2012.

In Connecticut, the all-Democratic delegation regularly coasts to victory. Lieberman’s old liberal nemesis, Lamont, won the governor’s race in 2018.

Nelson is the last Democrat to win a race for Senate or governor in Nebraska, back in 2006. He has found optimism recently in a very dark place, Jan. 6, trying to focus not on the riot but instead on the reconvening of Congress to certify Biden’s victory.

“This democracy is not going to be easy to topple,” Nelson said. “That’s the reason for hope. We could’ve had a different outcome.”